1. Field of the Invention
The present invention relates generally to a digital broadcasting system, and in particular, to a device and method for controlling channel switchover in a digital multimedia broadcasting (DMB).
2. Description of the Related Art
A motion picture experts group (MPEG)-2 transport stream (TS) is used as a transport standard of satellite or terrestrial DMB. A digital broadcasting center transmits program specific information (PSI) to a digital broadcasting receiver, and the digital broadcasting receiver switches-over a broadcasting channel with reference to the received PSI.
The PSI is carried in a number of tables including a program association table (PAT) and a program map table (PMT). The PAT includes an identification (ID) of a broadcasting channel on the air, and a packet ID (PID) having additional information of the broadcasting channel. The PMT includes a PID of
The audio or video TS of the corresponding broadcasting channel should be extracted for viewing a specific broadcasting. First confirm the PMT before obtaining the PID of the audio or video TS, and similarly the PAT is confirmed before obtaining the PID of the PMT. As such, a search is done of the PAT and the PMT to confirm the audio/video for purposes for viewing a broadcasting.
The PAT is set to have a transport period of about 0.5 seconds, and the PMT is set to have a transport period of approximately from 0.5 seconds to 1 second. The transport period depends on the digital broadcasting center. Transport is relatively frequently performed to minimize a channel switchover time. The PAT and the PMT should always be searched to switch the channel. Therefore, searching for the PAT and the PMT can take one or more seconds maximally. As a result, in a conventional art, the channel switchover time includes both an audio/video buffering time as well as a time taken to search for PSI data. Consequently, the channel switchover time is lengthened by the time taken to search for the PSI data.
FIG. 1 is a block diagram illustrating conventional demultiplexing in the digital broadcasting receiver.
If the digital broadcasting receiver receives TS packets, the TS buffer 22 buffers the received TS packets, following which; a PAT searcher 24 searches the buffered TS packets for a PAT. A header TS packet is analyzed to check whether the PID is ‘0’ to determine whether there is a packet having PAT information among the continuously received TS packets. A PID of ‘0’ represents that a payload has the PAT information.
From a successful search for the PAT, a PID list of a broadcasting channel and a PMT is obtained from the searched PAT, and a PID of the PMT of the and a PMT is obtained from the searched PAT, and a PID of the PMT of the broadcasting channel that a viewer desires to view is obtained. On the basis of the obtained PID of the PMT of the broadcasting channel that the viewer desires to view, a PMT searcher 26 analyzes the header of the TS packets buffered in the TS buffer 22 and confirms whether or not the TS packet is a corresponding PMT, thereby searching for the corresponding PMT.
Following a successful search for the PMT, a PID of an audio/video packetized elementary stream (PES) of the corresponding broadcasting channel is obtained from the searched PMT. Referring to the obtained PID of the video PES, a video TS packet of the corresponding broadcasting channel can be distinguished from the received TS packets. An intra frame searcher 28 can search the video TS packet of the corresponding broadcasting channel for an intra frame. If even the intra frame is searched, video/audio demultiplexing has only to be performed without a need to search for the PAT, the PMT, and the intra frame (this is because program information of the corresponding broadcasting channel has been searched). Simply, a video demultiplexer 30 confirms whether or not the TS packet is the video TS packet through the header analysis of the TS packets. If it is confirmed that the TS packet is the video TS packet, the video demultiplexer 30 performs the video demultiplexing and transmits the video data to a ring buffer (vid) 100. Even an audio demultiplexer 32 confirms whether or not the TS packet is an audio TS packet through the header analysis of the buffered TS packets. Upon confirmation that the TS packet is the audio TS packet, the audio demultiplexer 32 performs the audio demultiplexing and transmits the audio data to a ring buffer (aud) 150.
It is the intra frame searcher 28 that informs of the start of the audio/video demultiplexing. The intra frame searcher 28 searches for one perfect intra frame, and performs the demultiplexing including the intra frame. Therefore, the video demultiplexing can be performed only when the intra frame is searched, unlike the audio demultiplexing. There is an advantage in that the audio and video can be more easily synchronized with each other, if it is constructed to perform the audio demultiplexing after succeeding in searching for the intra frame as shown in FIG. 1.
The video or audio data is provided to each decoder (not shown), and each decoder decompresses a video or audio signal and outputs the decompressed video or audio signal through a display unit or a speaker for the viewer.
However, upon failure to search for the PAT, the buffered TS packets are discarded and the TS buffering and its subsequent steps are repeated. Upon success in searching the PAT but failure to search the PMT, the buffered TS packets are discarded and the TS buffering and its subsequent steps are repeated. Additionally upon success in searching for the PAT and the PMT but failure to search for the intra frame, the buffered TS packets are discarded and the TS buffering and its subsequent steps are again performed.
FIG. 2 illustrates an example for describing a video start time point based on the conventional demultiplexing.
On the assumption that the PATs are at 0.4 second, 0.9 seconds, and 1.4 seconds, the PMTs are at 0.3 seconds, 0.8 seconds, and 1.3 seconds, and the intra frames are at 0.1 second and 1.1 seconds, when the demultiplexing of FIG. 1 is performed, the PAT is searched at 0.4 seconds (1st), the PMT is searched at 0.8 seconds (2nd), and the intra frame is searched at 1.1 seconds (3rd).
As a result, at 1.1 seconds after the channel switchover, a first video TS packet is demultiplexed. However, even though the first video TS packet is demultiplexed, a picture is not directly displayed on a screen of the display unit. Until the video ring buffer (vid) 100 of a rear stage buffers the TS packet for about 1 to 2 seconds, the picture is not displayed. The picture starts displaying after about 3.1 seconds on the assumption that a buffering time is 2 seconds.